Highest CR for 87 Octane?
Thread Starter
On The Tree
Joined: Jul 2014
Posts: 143
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From: Lincoln, CA
Highest CR for 87 Octane? Sorry if this has been asked before but I haven’t had any luck with my searching… What is the highest compression ratio you would want to shoot for if running regular 87 octane gas? I have a 5.3 (LM7) that I’ll be swapping in to an older Blazer that I use for camping, hunting, and cruising around in the summer. The 5.3 will be getting a TBSS intake, Martin at Tick spec’d cam, and some 243 heads that I plan on milling to get the CR back up but I’m not sure what CR I should be shooting for since most of the gas stations I have to use out in the sticks only have 87 octane gas or diesel. Obviously this isn't a max effort build by any means but I want to do things right the first time and was planning on shaving off .020” and using some .040” Cometics to get around 9.9:1 since that’s what the newer trucks have and seemed like a pretty safe bet. I know a lot of guys on here try to go 10.5:1 or more but those guys are tuned for 91-93+ octane... What do you guys think?
I would stay under 10, if it's not a max effort engine then there's no need to go higher as you won't really miss the extra compression like you would on an all out racecar.
Take a look at what gas GM recommends for the newer trucks that are at 9.9:1 or the older LQ4 trucks which were right around 9.5:1.
Take a look at what gas GM recommends for the newer trucks that are at 9.9:1 or the older LQ4 trucks which were right around 9.5:1.
Thread Starter
On The Tree
Joined: Jul 2014
Posts: 143
Likes: 0
From: Lincoln, CA
Thanks guys. The newer trucks with the 9.9:1 CR still recommend 87 octane or better like my 5.3 so I'm thinking that's what I'll shoot for. I know compression helps make power so I wanted to do increase it as much as I can without sacrificing reliability. Running premium (91 octane out here) around town isn't a problem but I don't want to have to worry about detonation or anything else when I have to use the lower grade fuel up in the hills.
Running premium (91 octane out here) around town isn't a problem but I don't want to have to worry about detonation or anything else when I have to use the lower grade fuel up in the hills.
TECH Junkie
Joined: Dec 2005
Posts: 3,092
Likes: 11
I once saw a list of maybe 12 items by David Vizard that would help cut down on detonation. I remember quench, cool air intake charge and a cooler running motor as some of them. As stated above I would try to keep it under 10:1 and the last couple of ticks will not mean much power wise.
